Device and method for cooling a shot plug

ABSTRACT

The invention is accomplished by a shot block that is located intermediate the die and the shot sleeve. Such a shot block includes a body having mutually opposed first and second engagement surfaces. The first engagement surface abuts the shot sleeve and the second engagement surface abuts the die. A passage extends longitudinally through the body and defines an opening at the first engagement surface and an opening at the second engagement surface for transmitting a molten or semi-molten metal charge under pressure from the shot sleeve, through the passage, and into the die cavity. A cooling channel within the body circulates a fluid therethrough to absorb heat from the charge located within at least a portion of said passage (i.e. the biscuit).

RELATED APPLICATIONS

This application claims the benefit of priority from U.S. Provisional Patent Application No. 60/517,832 filed on Nov. 6, 2003.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for die casting parts, and more particularly, to a method and apparatus for die casting parts by cooling a shot plug or biscuit.

BACKGROUND

High-pressure die casting is an important process for manufacturing high volume and low cost components. Examples from the automotive industry include automatic transmission housings, piston heads, and gear box components. In this process molten or semi-molten metal (generally aluminum alloy) is injected at high speed (around 50 to 100 m/s) and under very high pressures through complex gate and runner systems and into a die.

In cold-chamber die casting, for which the present invention is particularly suited, molten or semi-molten metal is injected under pressure into hardened steel dies, often water-cooled. The molten metal, held in a separate furnace, is transferred by a ladle and poured into an extension tube, (generally called the shot sleeve), projecting from the entry point to the die.

A conventional die casting machine typically includes a die composed of a cover die half and an ejector die half. The cover die half and the ejector die half mate with one another along a separation surface and together define multiple die cavities. The cover die half is stationary, while the ejector die half is movable so that when a molten charge injected therein solidifies, the ejector die half can then be moved apart from the cover die half so that the solidified charge in each mold cavity can be removed.

Molten or semi-molten metal to be cast is charged into the die cavities by a charging assembly that includes a pressure cylinder or “shot sleeve” for receiving molten metal from an inlet, a piston movable in the shot sleeve for forcing the molten metal into the die cavities, and a shot block extending over the shot sleeve and connected to the die. The molten metal from the shot sleeve is supplied to the die cavities via passageways or “runners” defined in the separation surface between the cover die half and the ejector die half. Cooling flow passageways may be provided in the shot block for cooling the shot sleeve and thereby indirectly cooling the biscuit through the use of water, oil or other liquid as the cooling medium.

The plunger moves along the shot sleeve and pushes the molten metal through the shot sleeve and into the runner and die cavity. This molten charge (more material than is required to fill the casting) is used to force additional metal into the die cavity to supplement alloy shrinkage that takes place during solidification. Thus, in actual practice, the metal charge in the shot sleeve (typically referred to as a “biscuit”) will often still be molten, or at least partially molten, when the metal in the die cavities has completely solidified. The interconnected component and biscuit must sufficiently cool so as to form a solidified metal component consisting of the casting, runner, overflows, flash, and biscuit—as it is when removed from a die casting die. Once the metal in the mold cavities has solidified, the die halves are separated from one another and the solidified castings are ejected therefrom for further processing.

It is always desirable to shorten cycle times in the die casting operation to improve efficiency and increase production. And since the biscuit is typically the last component section to be sufficiently cooled prior to removing the component from the die, any increase in the cooling rate of the biscuit greatly influences shorter cycle times. Generally, the time it takes the biscuit to solidify sufficiently represents the constraining factor in achieving shorter cycle times in 25% to 50% of commercial die casting operations. Accordingly, there is a need in the art to achieve shorter cycle times by increasing the cooling rate of the biscuit before the die halves are separated.

The prior art has attempted to increase the cooling rate of the biscuit with little success. As described above, cooling lines have been provided in the shot block to dissipate heat from the end portion of the shot sleeve. While these cooling lines do remove some heat from the shot sleeve, often very little resultant cooling effect is provided to the biscuit.

Most importantly, it has been realized that the constant heating and cooling of the shot sleeve itself causes deformation or bowing therein. Such shot sleeve deformation or bowing can have damaging effects on the resultant die cast component.

Even during normal operation, a thin metal skin is often created on the interior of the shot sleeve formed from residual molten metal that cools and adheres to the shot sleeve passage. During repeated operation, the bowing of the shot sleeve can cause the plunger to scrape and break this skin which thereby creates particle impurities in the molten charge that can cause nucleation in the die cast component. As such, there is a need in the art to improve the cooling effect on the biscuit while also preventing the creating of particle impurities caused by the deformation or bowing of the shot sleeve.

SUMMARY OF THE INVENTION

The present invention includes numerous advantages and benefits over the prior art. Particularly, the present invention utilizes a shot block that does not encompass the shot sleeve as know in the prior art so that cooling effects provided by the shot block act directly upon the biscuit rather than indirectly on the biscuit through the shot sleeve. As such, improved cooling effects on the biscuit are realized to reduce overall cycle time of the casting operation. By reducing the length of the shot sleeve and providing cooling grooves in the shot block, cycle times can be reduced 10-15% and possible more.

The invention is accomplished by a shot block that is located intermediate the die and the shot sleeve. Such a shot block includes a body having mutually opposed first and second engagement surfaces. The first engagement surface abuts the shot sleeve and the second engagement surface abuts the die. A passage extends longitudinally through the body and defines an opening at the first engagement surface and an opening at the second engagement surface for transmitting a molten or semi-molten metal charge under pressure through the passage. A cooling channel within the body circulates a fluid therethrough to absorb heat from the metal charge located within at least a portion of the passage (i.e. the biscuit).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Objects and advantages together with the operation of the invention may be better understood by reference to the detailed description taken in connection with the following illustrations, wherein:

FIG. 1 is a cross-sectional view of a prior art cold-chamber die casting operation showing the shot sleeve within the shot block.

FIG. 2 is a cross-sectional view of the connection of FIG. 1 including drilled cooling lines in the shot block.

FIG. 3 is a cross-sectional view of the shot sleeve connection of a cold-chamber die casting operation according to the present invention.

FIG. 4 is a plan view of the shot block according to the present invention.

FIG. 5 is a cross-sectional view of the shot block of FIG. 4 taken along line A-A.

FIG. 6 is a cross-sectional view of the shot block of FIG. 4 taken along line B-B.

DETAILED DESCRIPTION OF THE INVENTION

In a typical cold-chamber die casting operation as shown in FIG. 1, molten metal is injected, under pressure, into hardened steel dies, often water-cooled. The molten metal, held in a separate furnace, is transferred by a ladle and poured into an extension tube or shot sleeve 10 projecting from a shot block 12. The molten metal is injected into a runner 14 formed by a runner block 16 and is thereby forced into the cavity formed by the dies.

Because the shot plug or biscuit 20 can be the determining factor in the cycle time of many casting operations, FIG. 2 illustrates a known attempt to increase the cooling rate of the shot sleeve 10 to thereby increase the cooling rate of the biscuit 20. Cooling lines 18 are formed in the shot block 12 and filled with a cooling solution, often water, to assist in dissipating the heat encountered by the shot sleeve 10. However, while this process assists in cooling the shot sleeve 10, it appears to have little effect on the rapid cooling of the biscuit 20 and does not generate significant cycle time reductions. In other cases where waterlines are not utilized, no significant increase in cooling effect on the biscuit 20 is achieved.

The present invention utilizes a similar construction as previously described. The present invention utilizes a construction where the biscuit is directly cooled via the shot block. Thus, the shot sleeve of the present invention does not extend within the shot block thereby indirectly cooling the biscuit through the shot sleeve as known in the prior art. Further, cooling channels or troughs are formed in the cover shot block and filled with a cooling solution, typically water, to dissipate heat from the biscuit. Therefore, the shortened shot sleeve provides direct cooling to the solidifying biscuit through the shot block via the cooling troughs. Such a construction also prevents the possible deformation or bowing of the shot sleeve, as described above, and the associated disadvantages related thereto.

With particular reference to FIG. 3, a die casting machine for creating a die cast component from a molten or semi-molten metal charge according to the present invention, generally designated as 40, comprises a die 42, a shot block 44, a shot sleeve 46, and a plunger 48.

Although any die configuration could be provide, generally a first die and a second die are configured for confronting engagement with one another along a separation surface and together define at least one die cavity therebetween. This die cavity is typically accessible through a runner 50. The shot sleeve 46 provides the molten or semi-molten charge to the die casting machine 40 by use of a plunger 48 or similar device. With a metal charge in the shot sleeve 46, the plunger 48 forces the charge through the shot block 44 and into the die cavity.

The shot sleeve 46 has a passage 52 therethrough for transmitting the metal charge. The shot sleeve 46 abuts the shot block 44 wherein the shot sleeve passage is in fluid communication with the shot block passage for transmitting the metal charge to the shot block passage. As shown in FIGS. 1 and 2, the prior art inserts the shot sleeve into the shot block for transmittal of the molten metal charge to the die cavities

The shot block 44 is located intermediate the die and the shot sleeve 46. The shot block 44 includes a body 51 having mutually opposed first and second engagement surfaces 53, 55. The first engagement surface 53 abuts the shot sleeve and the second engagement surface 55 abuts the die. A passage 54 extends longitudinally through the body 51 and defines an opening 57 at the first engagement surface 53 and an opening 59 at the second engagement surface 55 for transmitting a molten or semi-molten metal charge under pressure through the passage 54. A cooling channel 56 is located within the body 51 for circulating a fluid therethrough to absorb heat from the metal charge located within at least a portion of the shot block passage (i.e. the biscuit 60). The plunger 48, disposed within the shot sleeve passage 52, forces the metal charge through the shot sleeve passage 52.

With the shot block 44 located intermediate the die 50 and the shot sleeve 46, the plunger must be capable of entering the shot block passage 54 to continue to provide metal charge under pressure to the die cavity. As such, while the shot sleeve 46 abuts the shot block 44 and is held in place by convention means, the diameter of the shot block passage 54 is substantially similar and preferably identical to the diameter of the shot sleeve passage 52. Thus, the shot sleeve 46 will not enter the shot block passage 54 and the shot sleeve passage 52 will align with the shot block passage 54 to provide the molten charge. Further, such configuration will permit the plunger to travel through the shot sleeve passage 52 and into the shot block passage 54 to provide molten charge under pressure.

It is preferred that both the shot sleeve passage 52 and the shot block passage 54 be substantially cylindrical in configuration and have a consistent diameter. Further, it is preferred that the plunger has a diameter substantially identical to the shot sleeve and shot block passage diameters for improved transmittal of molten charge. However, it should be clear that any consistent configuration of the shot sleeve passage, the shot block passage, and the plunger will perform in the same manner, provided that their cross-sectional configurations are consistent. Such configuration could include, but are not limited to, square, rectangular, oval, circular, triangular, etc.

The device and method of the present invention is an improvement over the prior art by providing a shortened shot sleeve 46 so as to provide direct cooling to the biscuit via the shot block 44 having cooling channels 56. The cooling channel 56 is located radially outwardly from the shot block passage 54. As best shown in FIGS. 4 through 6, the cooling channel 56 extends longitudinally within said shot block 44 and extends at least partially circumferentially about the shot block passage 54. As such, the cooling fluid can be transmitted around at least a portion of the shot block passage 54 to dissipate heat in the biscuit 60 to promote increased cooling thereto. Therefore, heat transfer is optimized from the solidifying metal charge to gain a significant reduction in cycle time where the biscuit solidification time is the determinant. This technology can also be used in heavy runner blocks.

As indicated in FIG. 3, the shot block 44 can be manufactured using the Direct Metal Deposition (DMD) technique which utilizes a laser under CNC control to melt metal powder that rapidly solidifies (thereby providing a small heat-affected zone and a fine grain structure). Pass by pass, layer upon layer, the object is built up, finally resulting in the finished object.

While the invention has been described with reference to the preferred embodiment, other embodiments, modifications, and alternations that occur to one skilled in the art upon reading and understanding of this specification are covered to the extent that they fall within the scope of the appended claims. 

1. A die casting machine for creating a die cast component from a molten or semi-molten metal charge, said die casting machine comprising: a first die and a second die configured for confronting engagement with one another along a separation surface and together defining at least one die cavity therebetween; a shot block having a passage extending therethrough, said passage in fluid communication with said die cavity for transmitting a molten or semi-molten metal charge to said die cavity; a cooling channel within said body for circulating a fluid therethrough to absorb heat from said charge located within at least a portion of said shot block passage; a shot sleeve having a passage, said shot sleeve abutting said shot block wherein said shot sleeve passage is in fluid communication with said shot block passage for transmitting said charge to said shot block passage; a plunger disposed within said shot sleeve passage for forcing said charge through said shot sleeve; and wherein a cross-section of said shot sleeve passage is substantially equal to a cross-section of said shot block passage so that said plunger is capable of entering said shot block passage.
 2. The die casting machine of claim 2 wherein said shot block passage is substantially cylindrical.
 3. The die casting machine of claim 3 wherein said shot sleeve passage is substantially cylindrical.
 4. The die casting machine of claim 3 wherein said plunger has a cross section substantially equal to the cross-section of said shot sleeve passage.
 5. The die casting machine of claim 1 wherein said cooling channel is located radially outwardly from said shot block passage.
 6. The die casting machine of claim 5 wherein said cooling channel extends longitudinally within said shot block.
 7. The die casting machine of claim 5 wherein said cooling channel extends at least partially circumferentially about said shot block passage.
 8. A die casting machine for creating a die cast component from a molten or semi-molten metal charge; said die casting machine comprising: a first die and a second die configured for confronting engagement with one another along a separation surface and together defining at least one die cavity therebetween; a shot block having a generally cylindrical passage extending therethrough, said passage in fluid communication with said die cavity for transmitting a molten or semi-molten metal charge to said die cavity, said passage having a diameter; a cooling channel within said body for circulating a fluid therethrough to absorb heat from said charge located within at least a portion of said passage; a shot sleeve having a generally cylindrical passage with a diameter, said shot sleeve abutting said shot block wherein said shot sleeve passage is in fluid communication with said shot block passage for transmitting said charge therethrough to said shot block passage; a plunger disposed within said shot sleeve passage for forcing said charge through said shot sleeve; and wherein the diameter of said shot block passage is substantially equal to the diameter of said shot sleeve passage so that said plunger is capable of entering said shot block passage.
 9. The die casting machine of claim 8 wherein said cooling channel is located radially outwardly from said shot block passage.
 10. The die casting machine of claim 9 wherein said cooling channel extends longitudinally within said shot block.
 11. The die casting machine of claim 10 wherein said cooling channel extends at least partially circumferentially about said shot block passage.
 12. A shot block for use in a die casting machine wherein said shot block provides fluid communication of a molten or semi-molten metal charge between a shot sleeve and a die having a die cavity, the shot block comprising: a body having mutually opposed first and second engagement surfaces, said first engagement surface capable of abutting engagement with a shot sleeve and said second engagement surface capable of abutting engagement with a die having a die cavity; a passage extending longitudinally through said body and defining an opening at said first engagement surface and an opening at said second engagement surface for transmitting a molten or semi-molten metal charge under pressure through said passage; a cooling channel within said body for circulating a fluid therethrough to absorb heat from said charge located within at least a portion of said passage.
 13. The shot block of claim 12 wherein said passage is substantially cylindrical.
 14. The shot block of claim 12 wherein wherein said cooling channel is located radially outwardly from said passage.
 15. The shot block of claim 14 wherein said cooling channel extends longitudinally within said shot block.
 16. The shot block of claim 15 wherein said cooling channel extends at least partially circumferentially about said passage. 